Electrical terminal



NOV. 1, 1966 CARLSON 3,283,290

ELECTRICAL TERMINAL Filed April '7, 1964 HT'TORNEYS.

United States Patent 3,283,290 ELEtITRlCAL TERMTNAL Ernest R. (Iarlson, Fair-field, Courn, assignor to Harvey Hubbell, Incorporated, Bridgeport, Conan, a corporation of Connecticut Filed Apr. 7, 1964, Ser. No. 357,879 3 Qlaims. (Cl. 339-272) This invention relates to an improved electrical terminal, and particularly on one which is well suited for incorporation into the contact-terminal means of an electrical wiring device.

There are many prior art terminal constructions for connecting electrical conductors to the contacts of elec trical wiring devices. For example, the common screwtype terminal wherein an end of the conductor wire is stripped of its insulation and wrapped around the terminal binding screw, which is thereafter tightened so its head clamps the bared wire. There are other types of electrical terminal arrangements which avoid the necessity of stripping the insulation 011 the end of a conductor wire and wrapping it around a screw-type terminal, by including an insulation penetrating means; however, this type of terminal has numerous deficiencies, among which are its tendency to shear the conductor core and/0r make a defective electrical connection. Still other types of electrical terminal arrangements avoid the necessity of wrapping a bared conductor wire end around a terminal binding screw, by including a terminal clamping arrange ment wherein the bared end of an electrical conductor is inserted into a clamp-type terminal. Though clamp-type terminals eliminate many of the deficiencies of the screwtype terminals, a serious problem exists when clamp-type terminals are employed which is of such gravity that the electrical standard setting agencies will endorse clamptype terminals only within limited electrical capacity applications. The problem referred to is that of the clamping members in clamp-type terminals crushing the electrical conductor wire core, particularly stranded electrical conductor wire cores, and severing them, or at least a substantial number of their individual wire strands, thereby producing a defective connection at the terminal.

It is an object of this invention to provide an improved electrical terminal which is of the clamping type and possesses all of its advantages, but which is free of the heretofore existent deficiency of severing the wire strands of a stranded electrical conductor that it clamps.

Other objects of the invention are to provide an improved clamp-type electrical terminal individually and/ or in association wit-h an electrical wiring device, wherein a wide range of electrical conductor diameter sizes may be accommodated; the terminal may be disposed in a wiring device body so as to be Wholly confined within the Wiring device in which it is mounted; bending of the electrical conductor Wires is not required to secure them to the terminal, and the electrical conductor wire core may be placed in direct contact with the contact element of the wiring device.

Other objects and further details of that which I believe to be novel and my invention will be clear from the following description and claims taken with the accompanying drawing, wherein:

FIG. 1 is an end elevational view of the clamping means of the improved electrical terminal embodying the invention;

FIG. 2 is a sectional view taken substantially on line 22 of FIG. 1;

FIG. 3 is a longitudinal sectional view through an electrical terminal embodying the invention;

FIG. 4 is an end elevational view of the front of a modified clamping means;

3,23,2W Patented Nov. 1, 1966 ice FIG. 5 is a side elevational view thereof, with portions broken away and shown in section for clarity; and

FIG. 6 is a fragmentary sectional view of a wiring device showing an improved electrical terminal mounted therein.

With particular reference to FIGS. 1-3 of the drawings, one embodiment of the invention will be disclosed. In FIG. 3, a complete terminal assembly is illustrated; it comprises a terminal body 10 and a clamping means sub-assembly 12. The terminal body 10 may take various forms, but as illustrated it comprises a walled, box-like body having an internally threaded cylindrical opening 14 which is open at one of its ends 16 and closed at its other end by body wall 18. In a side wall 19 of the body 10 adjacent end wall 18, there is formed a relatively small opening 20 for insertion of the bared end of an electrical conductor into the interior of the terminal body. The terminal body 10 is preferably made of an electrical conducting metallic material, and may be connected in any convenient manner to the electrical conducting means to which it is desired to connect the electrical conductor wire. The terminal body 10 could be made of an electrical insulating material, if desired, as will become apparent when FIG. 6 is discussed.

In FIG. 3, electrical conductor wire C, which is of the stranded wire type, is shown clamped in the electrical terminal between the end wall 18 and the clamping means sub-assembly 12.

The clamping means sub-assembly 12, which can be most clearly seen by itself in FIGS. 1 and 2, comprises two elements, namely, a screw plug 24 and an eyeleted floating terminal plate 26 which it carries.

Screw plug 24 comprises a cylindrical plug having a diameter in excess of its axial extent; it is externally threaded at 28 and has a diametral kerf 29 formed in one axial side 30 to accommodate the end of a screw driving-type implement for axially adjusting the screw plug in the opening 14 when it is operatively mounted in the terminal assembly. To capture the screw plug in opening 14, the first thread at its end 16 is staked after the screw plug is disposed in opening 14. The other axial face 31 of the screw plug is flat, and a central plain opening 32 extends completely through the screw plug. The opening 32 flares radially outwardly at 34 and communicates with opening 36 that extends through the face 30 of the screw plug.

Terminal plate 26 comprises a member of thin sheetlike electrical conducting material having a circular disklike portion 38 arranged to be contiguous with and generally parallel to the face 31 of the screw plug and a cylindrical eyelet-like hub portion 40 that terminates at its free end in an outwardly flared retaining portion 42.

The terminal plate 26 is mounted on the screw plug 24- in such a manner, as illustrated, so as to be relatively rotatable in operation; its hub portion 40 is disposed in opening 32 of the screw plug so as to be rotatably supported by the screw plug, and its retaining portion 42 hugs the flared portion 34 of the opening 32 to maintain the terminal plate on the screw plug. It is the cooperative effect of the screw plug-terminal plate assembly, which comprises the clamping means sub-assembly, that largely produces the benefits of this invention. With reference to FIG. 3, when the clamping means subassembly is mounted in the terminal body and a stranded wire electrical conductor is inserted into the interior of the body through the access opening 20, it may be clamped firmly in position to effect the desired electrical connection by inserting a screw driver-like tool into the erf 29 of the screw plug 24 and turning it so as to advance the screw plug-terminal plate assembly toward the terminal body end wall 18. On engagement of the terminal plate disk-like portion 38 with the wire strands of the conductor C, a certain amount of frictional resistance to continued turning of the terminal plate 26 will occur; ordinarily, if the clamping means were a single screw plug, continued turning thereof would result in the compression of the conductor wire strands between the contacting end of the screw plug and the end wall 18, and in the severing of many of them as a result of the composite turning and compressive effect of the end of the screw plug. However, the unique construction of applicants clamping means sub-assembly prevents such damage to the conductor wire strands, by permitting the terminal plate to contact the conductor wire strands and to thereafter remain stationary, in a rotational sense, after sufficient frictional resistance is generated while simultaneously permitting the screw plug to continue to be rotated to cause axial advancement of itself and the terminal plate toward the end wall 18. The overall effect is to permit secure clamping of the stranded wire conductor without damaging it, as it is subject only to the axial closing compressive force of the terminal plate 26 and end wall 18 without the detrimental relative rotation of these parts.

In FIGS. 4 and there is illustrated another embodiment of the invention, including a modified form of clamping means sub-assembly which is similar to the one illustrated in FIGS. 1 and 2 in all respects other than that the terminal plate is modified; therefore, corresponding elements in the FIG. 4 and 5 embodiment to those of the FIGS. 1 and 2 embodiment are designated by the same reference numeral with a prime added. The major difference in the FIGS. 4 and 5 modification is that the disk-like portion 50 of its terminal plate 26' includes a plurality of circumferentially spaced, radially extending axial bulges or projections 52. The overall arrangement of the disk-like portion 50 0f the terminal plate 26' is such as to create a circumferentially sinuous formation that enhances the gripping of the wire strands of the electrical conductor and their clamping.

FIG. 6 illustrates an application of the improved electrical terminal of either disclosed embodiment into an electrical wiring device. A portion of the electrical wiring device body 60 is illustrated as including a notch 62 for receiving an improved terminal assembly. The terminal body illustrated in FIG. 6 is generally the same as the one illustrated in FIG. 3 except that it includes an enlarged opening 64 which permits the extension into the interior of the terminal body 10' of a serrated terminal leg 66 of an integral terminal-contact member 68. The member 68 is made of an electrical conducting material, such as metal, and has a contact leg 70 which is disposed in a contact opening 72 in the wiring device body in position to receive the cooperating contact member of a connectable Wiring device. As illustrated, the terminal-contact member 68 is disposed to assist in the mounting of the improved terminal assembly in the wiring device body notch 62 and, in turn, is clamped in proper position by a back plate 74 made of an electrical insulation material. In this structural association, the terminal body 10' can be made of an insulating material, such as a suitable plastic. The clamping means subassembly 76 in FIG. 6 may be of either form illustrated in FIGS. 1 and 2, and FIGS. 3 and 4.

In view of the foregoing, it will be apparent that applicant has provided an improved clamping means subassembly of general usefulness in electrical terminals possessing the major advantage of permitting very secure clamping of electrical conductors, including the delicate stranded wire type, without damaging them. Further, applicant has provided an improved electrical terminal satisfying all the objects of this invention. Certain aspects of my invention are not limited to the particular details of construction of the examples illustrated, and I contemplate that various and other modifications and applications will occur to those skilled in the art.

What I claim as new and desired to secure by Letters Patent of the United States is:

1. An electrical terminal comprising: a terminal body; said body having a clamping wall; an internally threaded cylindrical main opening formed in said body and extending therethrough to communicate with said wall; a lateral opening through said terminal body disposed adjacent said clamping wall and communicating with said main opening; a screw plug mounted wholly in said main opening for selective axial adjustment therein toward said clamping wall; means mounting said screw plug so as to be irremovable from said body; a central axial opening in said screw plug; a terminal plate made of thin sheet metal material and having a flat disk-like face portion and an eyelet-like hub portion; said hub portion disposed and loosely retained in said screw plug opening and including a flared portion for retaining said terminal plate on said screw plug, whereby said terminal plate is rotatably mounted relative to said screw plug so as to permit axial movement of said screw plug and terminal plate toward said clamping wall after said terminal plate contacts a conductor disposed in said terminal body between said clamping wall and said terminal plate unaccompanied by any rotational movement of said terminal plate relative to the conductor.

2. The electrical terminal of claim 1 wherein said terminal plate face portion includes circumferentially spaced axial bulges disposed to engage and enhance clamping of the electrical conductor.

3. The electrical terminal of claim 1 in combination with an electrical wiring device having a body including a space for housing said terminal; terminal-contact means including a terminal portion disposed adjacent said clamping Wall; and means for retaining said terminal and said terminal-contact means in said wiring device body.

References Cited by the Examiner UNITED STATES PATENTS 2,010,853 8/1935 Dyer.

2,285,928 6/1942 Jensen 339272 2,308,290 1/1943 Linton 24-135 X 2,697,391 12/1954 Gebele 339272 3,015,084 12/1961 Gribble 339272 3,173,739 3/1965 Carlson 339-21O FOREIGN PATENTS 1,215,113 11/1959 France.

953,794 4/1964 Great Britain.

BOBBY R. GAY, Primary Examiner.

PATRICK A. CLIFFORD, Examiner.

P. TEITELBAUM, Assistant Examiner. 

